Provenge
Fights Prostate Cancer

Prostate
cancer is one of the most common cancers. Each year in the US, around 230,000
men are newly diagnosed with prostate cancer and 30,000 die of the disease.

A
new form of immune therapy has shown a significant survival benefit in men who
have metastatic androgen-independent prostate cancer, when compared to patients
receiving placebo.

The
treatment is called Provenge (APC8015) and is manufactured by Dendreon
Corp. of Seattle. Provenge is called a vaccine, but unlike most vaccines,
it is used not to prevent illness but to treat an already existing condition.
The vaccine combines a protein that is found in most prostate cancer cells with
a substance that helps the immune system recognize the cancer as a threat. In
clinical trials, Provenge was well tolerated: the most common adverse events
that were reported were fever and chills lasting for one to two days.

The
vaccine is autologous in nature. That is, it is produced from the patient's own
cells and must be custom made for each patient individually. First, patients have
their blood run through a machine for two or three hours in order to extract certain
immune system cells, called antigen presenting cells (APCs). These cells are then
mixed with a protein called prostatic acid phosphatase (PAP) that is commonly
found on most prostate tumors. The PAP is fused with another immune-stimulating
substance called GM-CSF. The mixture is then returned to the patient in a one-hour
infusion. This process is repeated three times over the course of a month. The
basic idea is to alert the immune system that cells containing prostatic acid
phosphatase, (i.e., prostate cancer cells) should now be attacked as if they were
a foreign invader.

Antigen
presenting cells (APCs), a class of cells that includes dendritic cells and macrophages,
are of major importance in immunotherapy. They are distributed throughout the
skin, respiratory tract, and gastrointestinal tract. APCs serve two major functions:
they capture and process cell-surface markers, or antigens, for presentation to
the T class of lymphocytes. And they also produce signals that are required for
the proliferation and differentiation of those lymphocytes.

For
several years, dendritic cell vaccines have been offered at CAM-oriented clinics
in Mexico, the Caribbean and northern Europe, but have not been available in the
US outside the strict confines of clinical trials.

In
the latest study, men who were treated with Provenge survived on average
26 months, compared to 21.4 months for those who received only a placebo injection.
This may not seem like much, but in fact this 4.5-month median survival benefit
is said to be the longest ever reported from a Phase III study in advanced prostate
cancer. It is better than the roughly 2.5-month benefit that was shown in clinical
trials of Taxotere, a drug from Sanofi-Aventis. Taxotere is presently one of only
a few approved forms of chemotherapy for patients whose cancer has spread beyond
the prostate gland and is no longer responsive to hormonal therapy (the others
are estramustine and mitoxantrone).

What
is more, at three years, 28 of the 82 men who received Provenge were still
alive, compared to only 4 of 45 patients in the placebo group. Provenge
is now considered to have a shot at becoming the first anticancer therapy vaccine
to be approved by the Food and Drug Administration (FDA). Approval will
probably depend on the results of a larger study, currently underway, which should
be reported by the end of 2005.

"This
is provocative, it is promising. We now need to confirm this with an independent
study," said Dr. Philip Kantoff, a Harvard Medical School professor who heads
prostate cancer treatment at the Dana-Farber Cancer Institute in Boston. He was
not involved in latest company-supported study.

The
authors of the study emphasized the fact that the men who received the vaccine
were actually living longer. However, paradoxically, the study did not achieve
its primary goal of delaying the progression of the men's disease. This apparent
contradiction has caused some controversy. Some critics contend that "time
to progression" is the standard measurement of benefit and should have been
extended if the vaccine were truly helping men live longer. Dr. Kantoff described
his attitude as "skeptical."

But
according to Dr. Stephen Small, MD, professor of medicine and urology at the University
of California, San Francisco, who led the Phase III study, "Time to progression
is interesting, but it isn't the gold standard. The gold standard is survival.
We've improved survival....A therapy that prolongs life yet avoids the side-effects
of other therapeutic approaches is clearly attractive to patients and physicians
alike."

Dr.
Small pointed out that the time to progression was not the right measure to use
for judging cancer vaccines because cancer can worsen before the immune system
starts to fight it. He said that Provenge improved the survival of all patients,
not just those who had less aggressive cancers.

"The
survival benefit seen with Provenge is the largest ever reported in this
patient population with any therapy," said Dr. Small. "This survival
benefit, combined with a favorable safety profile, has the potential to provide
an important new treatment option for prostate cancer patients."

The
results were reported on February 19, 2005 at the Multidisciplinary Prostate Cancer
Symposium in Orlando, FL. Dendreon's stock price, which had been as high as $16
per share, sank in January when it was announced that the drug was failing to
attain its primary objective of delaying the time to progression. When word leaked
out about the survival advantage, its stock spike upward by 15 percent. However,
within a week it had returned to its recent $6-7 range. This may have been the
result of negative statements coming from others in the cancer research community.

According
to the Seattle Times, "the treatment has numerous skeptics."
These include Patrick Walsh, MD, a Johns Hopkins University urologist and a well-known
prostate-cancer surgeon, who said the study was too small to allow definitive
conclusions. He said it was unknown what other therapies patients may have had
during the three-year follow-up period, which may have made a difference.

"The
numbers here are just too small to make this a big deal," said Walsh. Dr.
Howard West, an oncologist at Swedish Medical Center, Seattle, said the study
would be a stronger statement if the survival edge was seen across a larger number
of patients. Still, he called the finding "extremely intriguing."

In
addition to Provenge, the company has another vaccine in development. This
is called APC8024 and targets HER-2/neu positive cancers, including those of the
breast, ovaries, colon and lung.

CancerDecisions.com
is directed by Ralph W. Moss, Ph.D. Dr. Moss is the author of eleven acclaimed
books including Antioxidants Against Cancer, Herbs Against Cancer, Questioning
Chemotherapy, and Cancer Therapy. He consults for thousands of clients through
his Moss Reports service. The
Moss Reports specializes in educating cancer patients about the most promising
alternative treatments for their condition.

Note
from Chet: Be sure to sign up for Dr. Moss's excellent newsletter at his website.

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